In order to verify the contribution of scanning electron microscopy to the taxonomic study of free-living amoebae, the authors studied at the encysted stage 21 strains of free-living amoebae representing 20 species (1 Naegleria gruberi, 1 Tetramitus rostratus and 18 Acanthamoeba sp). The method utilized is satisfactory for distinguishing the different genera. Using optical methods, it is possible to differentiate three groups (I, II, III) of Acanthamoeba, including 3, 10 and 5 species, respectively. The results obtained with scanning electron microscopy, however, are less precise. In particular, group II can be divided into only four sub-groups and group III into only two sub-groups and one species, A. culbertsoni. The method remains valid for group I.